The boat hull has been developing for thousands of years. The most important construction styles of wooden hull are clinker, caravel, and seam-frame. All these building styles necessitate a wooden skeleton of transverse ribs on which the planks are mounted and secured. They are made watertight by caulking with oakum, the pressure necessary for a watertight joint being produced by soaking the wood to swell it. In recent times special adhesives have been used.
The next stage of development was ship hulls of steel wherein the planking, formed of three-dimensional shaped steel plates, is secured by riveting to a steel skeleton. Calking and closely juxtaposed rivets make the joints watertight.
With the development of welding technology, welding is employed in modern-day construction of large boat hulls.
For small boats principally used for sporting purposes, shaped plywood is fitted to a positive form which corresponds to the shape of the hull. Subsequently longitudinal and transverse ribs are used as stiffeners and in the latest developments a sandwich is formed with two plywood forms and a foam body between them.
The use of synthetic resins has changed the building styles in the last 15 years and made possible mass production and considerable cost reductions.
According to this method a negative form, for limited production of wood and for more extensive production of metal, is manually laminated with glass matting saturated with polyester. This method allows the hull thickness to be matched to the load and allows the use of two-skin sandwich construction.
Most recently yachts are proliferating whose hulls are made of aluminum. In these up to now the method of steel production with welding to join shaped plates is chosen.
It has also been suggested to join extruded tongue-and-groove aluminum profiles by snapping them together with a sealant mass injected into the groove and riveting them to the ribs. This construction method is principally useful for small profiles and boats, since the profiles in the prebent condition cannot be fitted and joined together readily, so that a later bending to the ribs is necessary, which bending is only possible with small profiles without reinforced flanges as longitudinal ribs.